Open hearth furnace construction



'July 2, 1957 i A. usMlANl 2,797,910

OPEN HEARTH FURNACE CONSTRUCTION Filed March 10, 1954 4 Sheets-Sheet 2 ATTORNEY July 2, 1957 A. usMlANl 2,797,910

OPEN HEARTH FURNACE CONSTRUCTION Filed March 10. 1954 4 Sheets-Sheet 3 ATTORNEY ANDREW USMIANI.

United States Patent @PEN HEARTHFURNACE CNS'IRUCTION Andrew Usmiani, Weil-ton, W. Va., assigner to National SteeiCorporation, a corporation of Delaware Application March 10, 1954Serial No. 415,247

14 Claims; (Cl. 263-51) This invention relates to reducing furnaces and more particularly to furnacesof the type including regenerators employing checkerwork operable during one cycle for absorbing heat from the` hotV gases leaving the furnace and operable in another cycle giving up4 the stored heat to air on its way to the furnace.

Regenerators of the type employed in reducing furnaces, such as open hearth furnaces, include a chamber of' comparatively large volume lled with checkerwork made up of bricks of a material having goodi heat absorbing and dissipating characteristics. The bricks are arranged' in thechamber in such a manner as to provide a plurality of passageways for the, ow of gas through the checkerwork and to present a large area of the` brick surfaces to be contacted by the gases flowing therethrough. Generally, as inthe case of regenerators employed with open hearth furnaces, during one cycle of operations hot exhaust gases from the furnace are fed to the regenerator and ow in one direction through the passageways or the checkerwork,` giving up heat to the bricks. During the other cycle, the hot exhaust gases are directed through another regenerator, and air is fed through the heated regenerator in a direction toward the furnace. During its. passage through the passageways of the checkerwork, the air streams come into contact with the heated. bricks, absorb stored heat from. thel bricks, and leave the regenerator atan elevated temperature.

The hot exhaust gases from the furnace carry a considerable quantity of small particles of soot, dust and other matter, and when the exhaust gases. flow through the regenerator, the small particles are dislodged from the gas and collect on the bricks forming the entrance tothe checkerwork passageways, the collected particles being in somewhat of afused state due to the high temperaturesinvolved.. After an extended period4 of operation,.the magnitude ofthe deposits is such that the size of the entrances to the checkerwork passageways is so decreased that the rate of ow through the checkerwork necessary for efficient operation` cannot be maintained. It` then becomesnecessary to: shut down the furnace. and allow the regenerator chamber to coolto a low temperature, allowing workmen to enter. the regenerator chamber andclean the checkerwork passageways. This necessity of periodically shutting. down. furnace operation for checkerwork cleaning materially. reduces the furnace output, and the requirement of coolingthe regenerator to a low cleaning temperature constitutes a substantial loss in heat, and the overall eiciency of the installation would be` materially increased` if the periods of operation between cleaningV stoppagescould be increased.

It is therefore an object of the` present invention to provide a` novelfurnace installation of the. type including regenerators having checkerwork capable-of operation during extended periods between. periodic shut-downs for checkerwork cleaning.

Another Objectis to providea novel furnace installation ofthe above. type including. an arrangement for dislodging a portion of the small particles ofV dust, soot ICC and so forth from the hot exhaust gases prior to entry of the gases into the checkerwork and thus decrease the rate of deposit formation around the entrance to the checkerwork passageways.

Still another object of the invention is to provide a novel regenerator structure provided with auxiliary entrances for the checkerwork passageways adapted to be opened when the area. of the primary entrance is substantially reduced by deposits from the exhaust` gases.

Still another object is to provide aV regenerator structure of the above type in. which an arrangement is provided for opening the auxiliary entrances from without the regenerator during. normal operation of the furnace installation.

A still further object of the invention is to provide a novel regenerator arrangement for reducing the rate of deposit formation on the entrances to the checkerwork passageways and for increasing the length of the. operating period of the furnace. between furnace. shut-down for checkerwork cleaning, which may be incorporated in an existing regenerator without substantially decreasing the regenerator capacity.

Other objects and features of the invention will appear more fully from the following detailed description considered in connection with the accompanying drawings whichdisclose several embodiments of the invention. It 7is to be expressly understood, however,V that the drawings are designed for purposes of illustration only and not as a denition of the limits of the invention, reference for the latter purpose being had to the appended claims.

In the drawings, in which similar reference characters denote similar elements throughout the several views:

Fig. lis a diagrammatic presentation, partially broken away, of an open hearth furnace constructionv embodying the principles of the present invention;

Fig. 2 is a view in section of a regenerator, adapted for use with an open hearth. furnace, in. which the principles of the present invention are shown in greater detail;

Fig. 3 is a view in section. taken along the. line 3 3 of Fig. 2;

Fig. 4 is a view in section taken along the line 4 4 of Fig. 2;`

Fig. 5. is a diagrammatic sectional illustration of a. conventional regenerator installation in an open hearth furnace used as an aid in describing the present invention;

Fig. 6 is a sectional view of a regenerator constructed in accordance with another embodiment of the present invention; and.

Fig. 7 is a view in section taken along the line 7 7 of Fig. 6.

Referring more particularly to Fig. l of thev drawings,

an open hearth furnace embodying the principle of the present invention is disclosed therein, including a hearth 10. carrying a bath 11 of molten metal andv being pro.- vided with a front wall 12 having charging doors 13, and a back wall and a main roof, not shown. The port ends of the furnace each include end wall 14, side walls 15 and a port roof 16. Fuel burner enclosures 17 are centrally positioned in the port ends longitudinally of the hearth, and end uptakes 18. and 19 extend from the port ends onV both sides of the enclosures 17 into theslag pockets 20 formed by slag. pocket chambers 21 located beneath the port ends. The slag pocket chambers are provided with a fantail flue 22 leading to a regenerator chamber 23 housing checkerwork 24 and being connected to a tlue 25 communicating with the air supply or the exhaust stack. According. to the present invention, the fantail ilue 22 is connected tothe regenerator chamber 23 through an intermediate liuc 26, the'purpose of which will appear more fully below.

Open hearth furnaces ofthe foregoing type voperate on alternate cycles in order to utilize the heat in the combustion gases to preheat the incoming air and/ or gaseous fuel fed to the furnace. In one cycle the incoming air passes through the checkerwork in one of the regenerative chambers 23 where it absorbs heat from the checkerwork heated during the previous cycle and enters the furnace at one end through the uptakes 18, such as the left end as viewed in Fig. l. During this cycle the fuel burner in the enclosure at the left end of the furnace operates and the direction of the flame across the hearth is indicated by the arrows shown in Fig. 1, with the exhaust gases leaving the furnace by the uptakes 19 and passing through the regenerator chamber 23 wherein the checkerwork 24 absorbs heat from the hot gases. During the next cycle, the direction of the flows are reversed and the incoming air is caused to ow through the regenerative chamber 23 housing the heated checkerwork wherein the stored heat is given up to the air iowing therethrough, while the exhaust gases flow through and heat the checkerwork in the other regenerative chamber. These cycles are alternated upon operation of suitable valve means positioned in conduits connected between the lues 25 and the air supply and the exhaust stack in such a manner as to maintain eicient operation of the furnace.

The principles of the present invention embodied in the construction of the regenerators 23 and the intermediate ues 26 and their relationship with the slag pocket chambers 21 is shown more clearly in Figs. 2, 3 and 4. As shown, each regenerator is constructed on a suitable foundation, such as a reinforced concrete slab 30, and includes a floor 31, side walls 32, end walls 33 and 34, and a roof 35, forming a regenerator chamber for the checkerwork 24. The floor, roof and walls are constructed of suitable lire clay brick in accordance with conventional practice. The checkerwork 24 positioned in the regenerator chamber is made up of high-quality re clay bricks 36 having good heat absorbing and dissipating characteristics. The bricks 36 are positioned relative to each other to provide a large number of passageways in the checkerwork for the passage of gases through the regenerator chamber onto or away from the furnace so as to provide a large area of brick for contact with the gases for eiiicient heat transfer. The checkerwork may be formed by a plurality of Courses of transversely and longitudinally extending spaced bricks alternately stacked one on top of the other. The lowermost course 40 may comprise a plurality of transversely spaced coplanar double rows of bricks, one on top of the other, extending longitudinally of the regenerator chambeii. The rows of bricks forming the lowermost course S are supported on a plurality of longitudinally spaced members 41 extending transversely between the side walls 32. The members 41 are each supported by an arch member 42 bridging the side walls. The members 41 and 42 are spaced along the length of the checkerwork chamber and are located a substantial distance above the lioor 31 to provide a ue passageway 43 forming a communication between the flue 25 and the checkerwork. The second course of bricks 44 comprise double rows of bricks supported on the bricks of the rst course and extend transversely of the bricks of the first course. The second course of bricks are spaced longitudinally of the checkerwork chamber and extend transversely from side wall to side wall. The third course of bricks 45 is similar to the first course 41 and is supported by the second course 44. The checkerwork is thus made up of a plurality of longitudinally extending and transversely spaced courses of bricks and a plurality of transversely extending longitudinally spaced courses of bricks, alternately stacked one on top of the other to form a checkerwork of desired capacity in which the uppermost course of bricks 46 is spaced from the roof 35 a sufficient distance to provide line means 47 for the passage of fluid into and from the passages in thercheckerwork. In order that the alternate courses of bricks may be supported by courses of bricks immediately below, the longitudinal spacing of the transversely extending courses and the transverse spacing of the longitudinally extending courses are less than the length of the bricks making up the courses. In this way the bricks of the checkerwork are self-supporting.

Each course of longitudinally extending transversely spaced bricks forms a plurality of longitudinally extending transversely spaced passages 48, and each course of transversely extending longitudinally spaced bricks forms a plurality of longitudinally spaced transversely extending passages 49. Due to the alternate arrangement of the different courses of bricks, the longitudinally extending transversely spaced passages and the transversely extending longitudinally spaced passages are interconnected to form a plurality of tortuous passages through the checker- Work extending from the uppermost course of bricks 46 to the lowermost or iirst course of bricks 40. The ow of uid through the checkerwork between the flues 43 and 47 is in contact with a high percentage of the area of the bricks forming the checkerwork and provides a checkerwork having high heat absorbing and dissipating characteristics.

The entrances to the passageways extending through the checkerwork at the surface of the checkerwork adjacent the flue 47 are formed by the transversely extending longitudinally disposed spaces between the uppermost course of transversely extending longitudinally spaced bricks 46, the transversely extending spaces being divided transversely by the next lower course of longitudinally extending transversely spaced course of bricks. When the Huid passage through the checkerwork is such that the hot exhaust gases from the furnace flow through the checkerwork and then into the flue 25 onto the stack, the hot exhaust gases enter the passageways in the checkerwork from the ue 47 and pass through the passageway entrances formed by the uppermost course of bricks. As mentioned before, even though the hot exhaust gases pass downwardly through the slag pockets, the oxides and other dust particles carried by the hot exhaust gases are not completely removed prior to entry into the checkerwork. Consequently, as the hot exhaust gases pass through the passageway entrances in the uppermost courses, the oxides and other dust particles collect on the. bricks forming the uppermost courses. As operation of the furnace continues, the oxides and foreign dust particles continue to accumulate on the bricks, collecting in a fused mass, and the cross-sectional areas of the passageway entrances become smaller and the rate of gas flow through the checkerwork is decreased. Finally a degree of accumulation is reached in which the heat dissipating characteristics of the checkerwork is so impaired that the furnace must be shut down. Heretofore it has been necessary when this condition developed, to allow the regenerator structure to cool to a safe temperature for the workmen to enter the structure and remove the deposits. This procedure is time-consuming and materially reduces the furnace production, as a considerable period is required for the furnace to cool to a safe temperature.

As previously discussed, the present invention overcomes these disadvantages by providing an arrangement the utilization of which materially increases the operating period and hence the production output, of a regenerative type furnace between shutdowns for checkerwork cleaning. Briefly, the arrangement providedV by the present invention includes means operable Yfrom without the furnace when-at normal operating temperature for opening auxiliary entrances provided in the side wall of the checkerwork for the passage of hot exhaust gases into the passageways through the checkerwork without necessitating shutting down furnace operation, together with means for normally conducting the exhaust gases to the checkerwork past the auxiliary entrances in such a manner as to further remove oxides and other fine dust from the exhaust gases prior to their' entry into the checkerwork, and thus-further retard closing up of the normal entrancesto thepassageways.

The foregoing arrangement is shown more particularly in Figs. 2 and 3, in which the end wall 33 of the regenerator chamber is illustrated as terminating in a horizontal edge extending across the checkerwork chamber at a medial point of the checkerwork. The portion of the checkerwork above the medial point of the horizontal edge 50 is extended longitudinally of the checkerwork and is` terminated in an end face 51 coplanar with the outer surface 52 of the end` wall 33. Bricks 53 forming the end face 51 of the checkerwork function as structural members providing a support for'the courses of bricks above the horizontal edge 50, and a means for closing the one side of the transversely extending longitudinally spaced passages 49 adjacent thev end face. Bricks 54 of the end face 51 function as closure means for the ends of the longitudinally extending transversely spaced' passages 48.

For a purpose that will appear more fully below, the bricks 54 are removably secured in the end face 51 of the checkerwork, and are adapted to be pushed outwardly from the checkerwork beyond the end face. For this purpose the end wall 34 of the checkerwork chamber is provided with a plurality of removable plugs 55 located in the ends of the longitudinally extending, transversely spaced passages 48. Each of the passages 48 in each of the courses above the medial point of the horizontal edge 50 is provided with a removable plug. The plugs 55 are adapted to be removed from without. the regenerator to provide an opening 56 for the insertion into the checkerwork of an operating member S7 adapted to extend throughout the length of the checkerwork against the inside of the bricks 54 and knock the bricks 54 from the l end face 51.

The intermediate ue 26 is located between the fantail ue 22 and the checkerwork chamber to provide a path for the uids flowing therebetween. In addition, the intermediate liue provides a tortuous path for the hot exf and roof 35, respectively, of the regenerator chamber.

One end of the flue chamber 60 comprises the end wall 33 and the end face 51 of the regenerator, while a wall 64 forms the other end, the wall 64A extending upwardly from the floor 61 between the side walls 62 and terminating at a top edge 65 adjacent the upper passageway 66 of the fantail llue. A vertically disposed wall 67 extends from the roof 63 downwardly into the intermediate flue chamber substantially equally between the end walls thereof, to a point below the horizontal edge 50 of the wall 33. The intermediate wall may be supported by an I-bearn 68 extending between and being supportedv by the side walls. The wall 67 divides the upper portion of the intermediate flue chamber 6) into separate compartments 69 and 7); the compartment 69 communicating with the fantail flue and the compartment 70 communieating with the ue 47 feeding the top of the checkerworr and with both of the compartments communicating with each other through the lower portion of the intermediate flue chamber. With this construction, the hot exhaust gases flowing from the upper passageway 66 of the fantail are caused by the wall structure 67 to flow downwardly through the chamber 69 toward the low end of intermediate ue chamber 60 and into the low end of the intermediate flue chamber 60. The exhaust gases then How around the bottom edgeA 71 of the Wall 67 and upwardly, away, fromx the' low-end of the intermediate ue into the; chamber. 70A andfacross the end-face51 toward the iluey 47. Theintermediate ue chamber with the partition4 wall 67 thus directs the ow ofl hot exhaust gases on the, way to the regenerator across theY endface 51. Also,` the` tortuous path of the hot exhaust gases through the intermediate' ue chamber is effective in dislodgingl particles of fine dust from the hot exhaustv gases so that` the gases carry a smaller quantity of dust upon entrance-into: the'checkerwork. This feature materially reduces` the rate` of dust` accumulation on the bricks forming the entrances to the passageways of the checkerwork and. increases the operating time between which the furnace must be shut down for cleaning the checkerwork. The flue dust so dislodged from the hot exhaust gases fall to therbottomof: the intermediate ue chamber and collect onthe'oorf 61. These. particles may be removed while the furnace isin operation through a suit; able cleaningdoorway 72 Vprovided in the side wall. Also, the` bricks 54 which may be pushed outwardly fromy the end face 51 in the manner described above, fall downwardly-` in,y the intermediatetlue chamber and collect on the oor6l. These bricks may also be removed through the doorway 72.

The principles of,- the present invention may be 'applied to existing regenerators` without. substantially decreasing their capacity.; It has been determined that' the normal ow of hotk exhaust gases through conventional checkerwork is not through an appreciable portion of the checker- Work. adjacent the end wall of the regenerator chamber nearest the fantail flue. This is illustrated in Fig. 5 of the drawingsinrwhich the arrows indicate the normal path of tlowvl through the checkerwork which excludes the shadedportion 80. Since the portion is not inthe path of. the hot exhaust gases and cannot absorb heat, and-a hence cannot give'upheat to the incoming air, its presence has very little, if any, material effect upon regenerator efficiency. Consequently, the portion 80- of the; checkerwork may be removed from the regenerator andthe regenerator modified in accordance with the principles of the present invention by installing an intermediate lue of: the character described above, without materiallyr electing the eidciencyof the regenerator due to the decrease in the quantity` of checkerwork.

Another form of intermediate flue construction is shown in Figs. 6 and 7. In this construction a dividing wall 85,.-extending downwardly from the roof 63 a: part vv'ayy into the, chamber 60 and forming the chambers 69 and-.70, is constructed of tire bricks and supported on a masonry arch structure alsoV of re brick. The arch structure includes archways 86, 87 and 88 extending across the chamber 60 from side wall to side wall and beneath the. wall 88. One end of the archways 86 and 88 are supported by the side walls, while adjacent ends of the archways are supported by columns 89 and 90 constructed of. fire brick. s

In operation of an open hearth furnace including regenerators embodying the principles of the present invention, during one cycle of operation the hot exhaust gases from the hearth ilowinto one end port down the uptakes and into the slag pit, while the incoming air enters at the other end port of the furnace. The hot exhaust gases leave the slag pit through the fantail ue and enter the upper end of the. intermediate ilue. Upon entry into the intermediate' llueV the wall 67 causes the direction of ow of the hot exhaust gases to change abruptly and llow downwardly through the chamber 69 toward the bottom of the intermediate flue. In the lower end of the intermediateV ue the direction of flow again changes, with the exhaust gases flowing upwardly through the chamber 70 and across the end face 51 toward the roof 63 and into the llue 42. The tortuous path of the hot exhaust gases through the intermediate ilue causes a substantial per- 7 carried into the checkerwork. The dislodged dust particles collect on the floor of the intermediate ue an are removed therefrom through the doorway 72.

The hot exhaust gases, with a portion of the dust particles removed, enter the flue 47 and are conducted along the top of the checkerwork in communication with the entrances to the passageways through the checkerwork. The gases enter the passageways and flow through the checkerwork, giving up heat to the checkerwork, and enter the ue 43 beneath the checkerwork. From the ue 43 the exhaust gases ow from the regenerator through the flue 25 and are conducted onto the stack. During the foregoing air is caused to ow through the other regenerator onto the furnace; this regenerator having been previously heated by hot exhaust gas iiowing in the opposite direction. When the next cycle commences, the direction of flow through the regenerators is reversed so that the air now ows through the regenerator which was previously absorbing heat from the exhaust gases, and the other regenerator is heated up by the exhaust gases.

As mentioned above, during the cycle in which hot exhaust gases ow through the checkerwork, oxides, dust and other flue particlescollect in a fused state on the bricks in the uppermost course forming the entrances to the passageways. These deposits gradually'increase and eventually, if the process is allowed to continue, the cross sectional area of the entrance of the passageways through the checkerwork become so small that the resulting low rate of flow through the checkerwork materially effects regenerative action. However, according to the present invention, when the efficiency of the regenerator begins to drop, the operator removes the top course of removable bricks 54 in the end face 51 to provide an opening or an auxiliary entrance in the end face 51 leading to each of the Vlongitudinally extending passages 48. Thus the rate of flow through the checkerwork is maintained at an eicient rate.

After the operation continues, Vthe deposits on the bricks forming the entrance to the checkerwork passageways along the iiue 47 will continue lto increase and further block the rate of flow through the checkerwork Vby way of these entrances, and deposits will also begin to form around the openings in the end face 51, requiring additional auxiliary entrances to be formed in the end face. This is accomplished by removing the nextl course, or a portion thereof, of the removable bricks 54. As furnace operation continues, the bricks 54 are removed to form auxiliary entrances to the checkerwork passageways in such a manner asV to maintain sufficient regenerative action for eicient furnace operation.

The removable bricks 54 are removed from without the regenerator and when the furnace is in normal operation by removing a corresponding removable plug 55 in the opposite wall 34 of the regenerative chamber. When a plug 55 is removed, a suitable tool such as an elongated 'rod 100 may be inserted through the opening 56 in the the opening 56, and a similar process is followed for removing Vanother brick 54 to form an additional auxiliary entrance to the passageways of the checkerwork. As Vshown clearlyrin l, the region of the wall 34 of the regeneretor chamber` including the removable plugs is easily reached from thefloor 101.

Although two embodiments of the invention have been disclosed and described above, it is to be expressly understood that various changes Vand substitutions may be made therein Vwithout departing from the spirit of the invention, as well understood by those skilled in the art. Reference therefore will be had to the appended claims for a definition of the limits of the invention.

What is claimed is: l. A regenerator for abstracting heat from a stream of hot gas flowing therethrough in one direction and for dissipating the abstracted heat to a stream of relatively colder gas owing therethrough in the opposite direction, comprising a checker chamber, checkerwork formed of heat ahstracting and dissipating material located in the checker chamber, the checkerwork presenting a plurality of passageways therethrough for the passage of substreams of a stream of gas flowing through the checker chamber, means forming a first flue communicating with the passageways of the checkerwork, and means including a side wall of the checker chamber forming a second flue connected to the first ue for conducting the gas stream past the outside surface of the side wall on its way to and from the passageways of the checkerwork, the side wall of the checker chamber including a plurality of removable plugs filling entrances between the second flue and the passageways of the checkerwork.

2. A regenerator for abstracting heat from a stream of hot gas flowing therethrough in one direction and for giving up the abstracted heat to a stream of relatively colder gas flowing therethrough in the opposite direction, comprising a checkerwork chamber, checkerwork formed of heat abstracting and dissipating material located in the chamber, the checkerwork presenting a plurality of passageways for the passage of streams of gas therethrough, means forming a first line in communication with one end of the passageways, means forming a second flue in cornmunication with the other ends of the passageways, means including a side wall of the Checker chamber forming a third flue connected to the second flue for conducting gas past the outside surface of the side wall on its way to and from the passageways, the side wall of the chamber including a plurality of removable plugs filling entrances between the third flue and the passageways of the checkerworks, and means operable for removing the removable plugs from without the checkerwork chamber and from without the third liue.

3. A regenerator for abstracting heat from a stream of hot gas flowing therethrough in one direction and for gving up the abstracted heat to a stream of relatively cold gas flowing therethrough in the opposite direction, cornprising a checker chamber, checkerwork formed of heat abstracting and dissipating material located in the checker chamber, the checkerwork forming a plurality of passageways for the passage of streams of gas therethrough, means forming a first flue in communication with one end of the passageways, means forming a second flue in communication with the other ends of the passageways, means including a side wall of the chamber forming a third flue connected to the second flue for conducting gas past the outside surface of the side wall on its way to and from the passageways, the side wall of the chamber comprising a portion of the checkerwork and including a plurality of removable plugs to present a continuous surface, the removable plugs filling auxiliary entrances between the third flue and the passageways of the checkerwork.

4. A regenerator of the character set forth in claim 3 including means operable to permit selective removal of the removable plug from without the regenerator.

5. A regenerator for abstracting heat from a stream of hot gas flowing therethrough in one direction and for Ygiving up the abstractedV heat to va stream of relatively `heat abstracting and dissipating material in the checker chamber, the checkerwork presenting a plurality of vertically disposed passageways for the passage of streams of gas therethrough, means forming a first ue located below 'the checkerwork in communication with the passageways,

agzavgmo .9 means forming a second flue located? above the. checkerwork in communication withthe passageways, meansincluding a side wall of the chamber forming a third flue connected to the second iiue for conducting gas past the:outside surface of the side wall on itsway to and'from the passageways, the side wall including a plurality of removable plugs filling entrances between the third flue and the passageways of the checkerwork.

6. A regenerator for abstracting heat from a stream of hot gas owing therethrough in one direction and for giving up the abstracted heat to a stream of relatively colder gas owing therethrough in the opposite direction, comprising a checker chamber, checkerwork formed of heat abstracting and dissipating material located in the checker chamber, the checkerwork presenting a plurality of vertically disposed passageways for the passage of a stream of gas therethrough, means forming a first ue positioned below the checkerwork in communication with the passageways, means forming a second ilue positioned above the checkerwork in communication with the passageways, means including a side wall of the checker chamber forming a third ue connected to the second ue for conducting gas past the outside surface of the side wail on its way to and from the passageways, the upper portion of the side wall of the checker chamber including a plurality of removable plugs, each of the removable plugs filling a passage between the passageways of the checker chamber and the third flue.

7. A regenerator for abstracting heat from a stream of hot gas flowing therethrough in one direction and for giving up the abstracted heat to a stream of relatively colder gas flowing therethrough in the opposite direction, comprising a checker chamber, checkerwork formed of heat abstracting and dissipating material located in the checker chamber, the checkerwork presenting a plurality of vertically disposed passageways for the passage of streams of a gas therethrough, means forming a first iiue positioned below the checkerwork in communication with the passageways, means forming a second ue positioned above the checkerwork in communication with the passageways, means including a side wall of the checker chamber forming a third ue connected to the second iiue for conducting gas past the outside surface of the side wall on its way to and from the passageways, the side wall of the checker chamber having an upper portion including a plurality of removable plugs, the removable plugs lling passages between the passageways of the checker chamber and the third flue, and means operable for selectively removing the removable plugs from without the checker chamber.

8. A regenerator of the character set forth in claim 7 in which the upper portion of the side wall of the checker chamber includes a plurality of vertically spaced series of removable plugs, with each series comprising a plurality of removable plugs extending in spaced relation across the side wall.

9; In an open hearth furnace, a hearth, a checker chamber, checkerwork in the chamber forming a plurality of passageways for the passage of gas through the checker chamber, a closed chamber connected to the hearth and to the checker chamber for conducting a gas stream between the hearth and the checker chamber, the checker chamber and the closed chamber having a common side wall over which the gas stream iiows as it passes through the closed chamber between the hearth and the checker chamber, and a plurality of removable plugs in the common side wall, the removable plugs filling passages forming communication between the passageways and the closed chamber.

10. In an open hearth furnace, a hearth, a checker chamber, checkerwork in the chamber forming a plurality of passageways for the passage of a gas through the checker chamber, means forming a flue communicating with the passageway, a closed chamber connected to the hearth and to the flue, for conducting a gas stream between the'l hearth and" thel checker* chambe'n. thechecker chamber` andthe. closed chamber hav-ing a common side wall over which the gas stream flows'as-it passesthrough the closed chamber between the hearth and the ue, the commonrside wall including a plurality of removable plugs filling passages communicating between theV passageways of the checkerwork and the closed chamber.

11. In an open hearth furnace, aY hearth, a checker chamber, checkerwork in the chamber forming a plurality of passageways for the passage of a gas through the checker chamber, a ue communicating with the passageways, a closed chamber connected to the hearth and to the flue for conducting a gas stream between the hearth and the checker chamber, the checker chamber and the closed chamber having a common side wall over which the gas stream ows as it passes through the closed chamber on its way between the hearth and the ue, the common side wall including a plurality of removable plugs filling passages forming communication between the passageways and the closed chamber, and the closed chamber including means for providing a tortuous path for the gas stream from the hearth to the checker chamber.

12. In an open hearth furnace, a hearth, a checker chamber having a roof, checkerwork positioned in the checker chamber and having an upper surface and formed to provide a plurality of vertically disposed passageways for the passage of streams of gas through the checker chamber, the checkerwork being positioned in the checker chamber with its upper surface spaced below the roof of the checker chamber to provide a flue communicating with the passageways, a chamber forming a slag pocket communicating with the hearth, the chamber having a roof joined to the roof of the checker chamber and a side wall common with the checker chamber, the common side wall including an upper end lying in a plane spaced below the roof of the checker chamber to establish communication between the flue and the chamber, the common wall including a plurality of removable plugs filling passages between the chamber and the passageways of the checkerwork, and a partition member in the chamber extending downwardly from the roof of the chamber in spaced relation with the common wall to form a tortuous path through the chamber for the gas stream on its way between the hearth and the checker chamber.

13. In an open hearth furnace, a hearth, a checker chamber having a roof, checkerwork positioned in the checker chamber having an upper surface and formed to provide a plurality of vertically disposed passageways for the passage of streams of gas through the checker chamber, the checkerwork being positioned in the checker chamber with its upper surface spaced below the roof of the checker chamber to provide a flue communicating with the passageways, a chamber forming a slag pocket, the chamber having a roof joined to the roof of the checker chamber and a side wall common with the checker chamber, the common side wall including an upper end lying in a plane spaced below the roof of the checker chamber to establish communication between the iiue and the chamber, the side wall of the chamber opposite the common wall having an upper end lying in a plane spaced below the roof of the chamber to provide an entrance to the chamber communicating with the hearth, the common wall including a plurality of removable plugs located in its upper portion filling passages communicating between the chamber and the passageways of the checker work, and a partition member in the chamber extending downwardly from the roof of the chamber in spaced relation with the common wall and the other side wall of the chamber to form a tortuous path through the chamber for the gas stream on its way between the hearth and the checker chamber.

14. An open hearth furnace as defined in claim 13 in which the side wall of the checker chamber opposite the common wall is provided with removable members located References Cited in the le of this patent UNITED STATES PATENTS Chapman Apr. 14, 1925 12 Smalley Feb. 22, 1938 Dean Aug. 9, 1938 Morton Oct. 17, 1939 Hiller et al. Dec. 1, 1942 Thorpe Apr. 12, 1949 Drake July 3, 1951 

